Chemical vapor deposition and submicron etching techniques are widely applied, for example, in the manufacture of semiconductors and chips. Existing methods typically afford limited control over the collimation of the deposited or etching materials impinging on the substrate, resulting, for example, in overly broad reaction zones or lower than desired aspect ratios (i.e., coating or etching depth divided by width). There is considerable interest in developing spatially resolved deposition processes.
Gas-surface reactions are multistep processes that involve complex interactions between a solid substrate and gas-phase reactants. The nature of these interactions can vary with the system. While many reactions depend sensitively on the geometric and electronic structure of the substrate, others appear to depend more strongly on the extent of excitation in the gas-phase reagent. For example, the direct dissociative chemisorption of methane, which is rate limiting in the industrial steam reforming reaction, is an example of the latter case.
Dissociative chemisorption is affected by a number of parameters that complicate experimental efforts to unravel the reaction mechanism. Translational, vibrational, and rotational energy in the gas-phase reagent, surface temperature, surface structure, and the orientation and impact parameter of the incident gas-phase molecule can all affect the outcome of the gas-surface encounter.